Thread: Pressure Mat Hack...Still Confused

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So, I have seen a few threads discussing how to hack a pressure mat trigger and it's like Greek to me. While I am handy/crafty and generally creative, I know absolutely nothing about electricity or wiring and would really appreciate if someone could please explain in step-by-step fashion how to hack one of these types of mats to trigger say a wiper motor to go on and off.

http://www.harborfreight.com/pressur...mat-96481.html

My 2 concerns are that is 1) safe and 2) reliable.

Thank you GREATLY in advance!

I hear ya man...#1 rule is DON'T overthink it! I'll use the Talking Boris for an example. The "try me" plug is what you'll hack into. First, cut the white wires just below the alarm on the harbor freight pressure pad, strip them to expose the two wires. step two...Cut off the button end of the Boris, strip the two wires and simply connect them to the alarm unit, plug 'er in!

I'm guessing the 9-volt battery is for the alarm box, so you shouldn't need that. Just remember if you hook a motor to the switch mat, it will only turn when someone is standing on the mat.
Just cut off the alarm box and seperate and strip the two wires going to the mat. Find one of the power wires going to your motor (or whatever device) and snip one of those wires (either the positive or the negative) in half. Strip both ends of the motor wire you just cut and solder (or tape) one each of the switch mat wires to one each of the motor wires. Apply the power and the device should activate when the mat is stepped on.
Just a warning--I bought a Screaming Mat at Big Lots last Halloween for hacking. I cut off the screaming box, but the mat would not work to activate any other device and I don't know why. Hopefully the mat from Harbor Freight isn't designed the same way.
I just make my own switch mats out of aluminum foil and wire.

Wow. Thank you! It's all so clear to me now. All the pad does it complete the circuit when stepped on. I was TOTALLY over thinking it. Thanks again!

Just a quick update...I received my Harbor Freight alarm pad in the mail today. I spliced the wires as instructed and now successfully have the mat switch turning my monster in a box on and off. So, it is essentially switching a red light bulb, computer speakers and wiper motor on and off. It's pretty sweet.

The only problem is the red light comes on immediately, however the wiper motor and PC speakers lag behind a few seconds. I suppose because they need more juice. Any suggestions on how to make it so they all 3 fire off immediately?

Thanks again!

Hello, this is Bozz’s son; I’ve been tinkering with electrical engineering for a few years now, and have been assigned the problem of hacking the various pressure mats.

After testing both the Harbor Freight and Spirit pressure mats, I have concluded that they are different types of mats. By checking the resistance of the mats, we can see that the Harbor Freight mat is acting like a simple momentary switch; lowering in resistance when pressure is applied. However, the Spirit mat shows no change in resistance, but produces an impulse of voltage when pressure is applied. This implies that the Spirit mat is a piezoelectric transducer (http://en.wikipedia.org/wiki/Piezoelectricity, http://en.wikipedia.org/wiki/Piezoelectric_sensor); and should not function with props that require a closed circuit. It may be possible to build a simple trigger circuit for the Spirit mat using an amplifier and FET transistors.

Haha! Bozz's son is way over my head, the explantions by Daveinthegrave and Croglinvampire make much more sense to me - I'm much like DeadbyDawn, I like things simple like, as he explains.

Originally Posted by bozz

Hello, this is Bozz’s son; I’ve been tinkering with electrical engineering for a few years now, and have been assigned the problem of hacking the various pressure mats.

After testing both the Harbor Freight and Spirit pressure mats, I have concluded that they are different types of mats. By checking the resistance of the mats, we can see that the Harbor Freight mat is acting like a simple momentary switch; lowering in resistance when pressure is applied. However, the Spirit mat shows no change in resistance, but produces an impulse of voltage when pressure is applied. This implies that the Spirit mat is a piezoelectric transducer (http://en.wikipedia.org/wiki/Piezoelectricity, http://en.wikipedia.org/wiki/Piezoelectric_sensor); and should not function with props that require a closed circuit. It may be possible to build a simple trigger circuit for the Spirit mat using an amplifier and FET transistors.

Interesting! What voltage is present on the Spirit mat? Enough to operate a relay or would a MOSFET, like an IRF510, be needed?

With a R test of up to a volt was present. It would be possible to operate a MOSFET with the pad. However the pad produce an impulse (with a very small amount of current), so a locking relay or a trigger circuit (556 monostable) would be neccessary. Off to school now but I have more info to share later. PS,.....my boy is only 15 going on 20.....ha...ha......but this is his favorite hobby.